1. Field of the Invention
The present invention relates to a biometric information input apparatus for conducting personal authentication or pointing by the use of biometric information such as a fingerprint or a palmprint. More particularly, the invention relates to a biometric information input apparatus of the sweep type for entering biometric information while causing a relative displacement of a living body.
2. Description of the Related Art
Along with the recent tendency toward higher functions, compact information devices such as cell phones and PDAs (Personal Digital Assistants), it is now possible for these devices to be connected to systems or to store a huge volume of personal information, and there is an increasing demand for a higher security performance in these devices.
In order to ensure a high security in these devices, personal authentication based on biometric information has a high reliability and can satisfy the above-mentioned increasing demand. Particularly, use of fingerprint as biometric information can provide a high serviceability.
When carrying out personal authentication by use of fingerprint as biometric information, fingerprints are sampled as image information from fingers of the person to be authenticated (a pattern composed of ridges which can be in contact with the sampling surface of the fingerprint sensor and valleys not coming into contact with the sampling surface). Positional information of bifurcations and ridge endings is extracted as feature information from, for example, a ridge image of the fingerprint image, and personal authentication which determines whether or not the person to be authenticated is the person in question is accomplished by matching the thus extracted feature information with registered feature information of the person to be authenticated registered in advance.
As a fingerprint sensor downsized for mounting on a compact information device such as a cell phone or a PDA, there is known a sweep-type (scanning type) fingerprint sensor (Re: J P 10-091769, JP 11-253428 and JP 2005-143890). The sweep-type fingerprint sensor has a rectangular detecting surface which is sufficiently smaller in length than the finger length and has a small area) (sensor area/pickup surface). A plurality of partial images of fingerprints are continuously sampled by means of the fingerprint sensor while moving the detecting surface (fingerprint sensor) relative to the fingers, and a whole view of fingerprint images is re-configured from the sampled plurality of partial images.
Information of minutiae (bifurcations of ridge, ridge endings, etc.) is extracted and generated from the thus re-configured fingerprint image, and the above-mentioned personal authentication is accomplished on the basis of this information.
Available related patent documents are as follows:
In such a conventional sweep-type fingerprint sensor, however, scanning may sometimes be carried out in a wetted state of finger, with, for example, fingers having drops of water caused by sweat, depending upon the environment or circumstances of use. Such a case leads to a problem in that sweat or water drops are picked up in the fingerprint image, and finger displacement causes generation of a string-shaped pattern, thus deteriorating authenticating performance as noise when conducting a personal authentication.
More specifically, when scanning a wetted finger by a sweep type fingerprint sensor, moisture held between the finger and the sensor is entangled by the moving finger or sweat adheres to the sensor while the finger moves, resulting in a longitudinal string-shaped image pattern in the fingerprint image. This longitudinal string-shaped image pattern is low in reproducibility, or has not relationship with the fingerprint pattern at all, forms noise in the case of personal authentication and degrades the authenticating performance.
This noise of image pattern caused by a wetted finger can be inhibited or removed through image processing, but implementation of such an image processing requires much time and labor for research and development, and further for industrialization, thus leading to the problem of an inevitable increase in cost.